1. Field of the Invention
The present invention relates to a polishing process and a polishing apparatus for polishing the end face of an optical connector assembly with at least one optical fiber.
2. Description of the Related Art
When connecting at least two optical fibers in a detachable manner, the technique is employed of attaching optical connectors to the ends of the optical fibers to be connected and mating the end faces of two optical connector assemblies with the optical fibers. When connection is performed by this method, to raise the precision of connection of the optical fibers and ensure smooth transmission of the optical signals, it is necessary to polish the end faces (connection faces) of the optical connector assemblies with the optical fibers so as to ensure the end faces are flat and smooth.
Most general polishing process is a polishing process for polishing the end face of the optical connector assembly with the optical fibers by abrasive grains. In accordance with the conventional polishing process, in the first polishing step, use had been made of a grinding process using fixed abrasive grains so as to efficiently remove the adhesive adhering to the end face of the optical connector with the optical fiber, but in the later steps, the conventional practice had been to polish the end face of the optical connector by placing diamond and other abrasive grains on a buff etc. The polishing process based on the use of abrasive grains as employed in the later steps is called a polishing process using free abrasive grains, since the polishing step is performed with the abrasive grains not fixed to a buff or other polisher.
If optical fibers made of hard quartz glass and an optical connector made of soft plastic etc. are polished together such as the optical connector assembly with the optical fibers by a polishing process using free abrasive grains, the abrasive grains, which can move with respect to the buff or other polisher, will tend to collect at the soft material portion, that is, the end face of the optical connector, and there is thus the problem of more of the optical connector being cut away and the ends of the optical fibers sticking out.
In the case that sufficient flatness of the ends of the optical fibers is not secured, even if two optical connector assemblies are attempted to be joined, it is extremely difficult to bring the end faces of the optical fibers into direct contact. This connection error results in a larger connection loss and has an adverse effect on the transmission of the optical signals.
Further, if the optical connector assemblies are repeatedly attached and detached, there is liable to be damage to the ends of the optical fibers sticking out from the end face of the optical connector assembly and there is thus a problem with durability. Also, each time the optical connector assembly is attached or detached, the connection loss due to the connection error differs and thus there is a problem in reproducibility as well.
In particular, when connecting a multiple optical fiber bundle comprised of a bundle of a plurality of optical fibers, in addition to the above-mentioned problem, that is, the problem of the ends of the optical fibers sticking out from the end face of the optical connector, the lengths by which the optical fibers stick out from the end face of the optical connector assembly will also often differ.
Also, in the polishing process using free abrasive grains, even if the polishing speed is increased so as to raise the productivity of the polishing, slippage occurs between the abrasive grains and the buff or the end face of the optical connector assembly, so that the amount of polishing is not necessarily proportional to the polishing speed and there is the problem that the polishing time becomes longer and the polishing efficiency drops.
Further, with a polishing process using free abrasive grains, the abrasive grains (diamond etc.) used are discarded after each polishing step, so there is the problem of a high polishing cost.
On the other hand, in superprecision polishing technology, there is known a polishing process using so-called fixed abrasive grains where the polishing work is performed using a polisher with fixed abrasive grains. The conventional polishing process using fixed abrasive grains, however, adopted the technique of so-called feed control, where the polishing was performed while feeding the workpiece to the abrasive wheel.
If a brittle material like glass is polished by this feed control system, the range of brittle fracture becomes larger and scratches and other damage given to the workpiece are often seen. To eliminate this problem, fine and precise feed control of a level of tens of nm is required, so it is necessary and essential to employ a polishing apparatus having a high rigidity and a complicated control apparatus. There were therefore problems with cost and installation space. Accordingly, the polishing process using the fixed abrasive grains is almost adopted in the polishing process for the optical connector assembly. As one example, the Japanese unexamined Patent Laid Open Publication No. 3(1991)-196956 discloses the polishing process for the optical connector assembly using the fixed abrasive grains.
In the polishing process disclosed in the Japanese reference No. 3-196956, however, sufficient flatness of the ends of the optical connector assembly is not secured so as to result in a larger connection loss, if a polishing apparatus having a high rigidity and a complicated control apparatus are not employed.
The polishing process disclosed in the Japanese reference No. 3-196956 is briefly shown as FIG. 20 (a) to (e). As shown in FIG. 20, a top face "a" to "b" of workpiece 102, which is an optical connector assembly, is ground by a cup-shaped grinding wheel 100. In this process, actual grinding quantity "A" is shown as the following formula. EQU A=x-y
In the formula, "x" is a cutting quantity for grinding and "y" is elastic strain of the apparatus.
In this process, contact area of the grinding wheel 100 and the workpiece 102 changes and thereby grinding resistance changes in accordance with feeding of the workpiece into the grinding wheel. As a result, deflection of the apparatus changes and thereby actual grinding quantity changes in accordance with feeding of the workpiece, so that sufficient flatness of the ends of the workpiece 102 is not secured as shown in FIG. 21 which shows the flatness tendency.
Further, as shown in Japanese unexamined Patent Laid Open Publication No. 2 (1990)-131204, polishing film is used in a polishing process for an optical connector assembly. In this process, abrasive grains are easily to be dropped off from the polishing film, and thereby it is difficult to administrate the quality of the polishing process. As a result, it is difficult to secure efficient flatness of the optical connector assembly.